The present invention relates to a switch control method for dual tone multi-frequency (DTMF) service of a mobile switching center (MSC), in which a number connected to an automatic recording service (ARS) system is dialed to push a corresponding service code so that a mobile subscriber receives information from the ARS system
In the conventional public switched telephone network (PSTN) or integrated service digital network (ISDN), the coding of voice and tone is performed in a pulse code modulation (PCM) mode in which sampling is carried out at 8 kHz and the bit rate is above 64 kbps so that the DTMF tone from a terminal can be transmitted directly to the counterpart.
For prior art related with the conventional DTMF device, there is suggested U.S. Pat. No. 4,922,528 entitled "Dual tone multi-frequency signal recognizer for telephone mobile exchange". This disclosure uses several bandpass filters corresponding to the respective numbers as a signal detecting circuit. The respective output signals are compared with one output signal within two frequency domains. This technology enables detection of vocal signal frequency to become reliable.
There is also presented U.S. Pat. No. 4,856,759 entitled "Identifying words entered on dual tone multi-frequency". In this reference the discrimination of words entering the DTMF push button is decided in two or three frequency groups.
As mentioned above, in the DTMF service of PSTN, the DTMF frequency is transmitted through a DTMF telephone while the communication path is connected, and the counterpart mobile exchange recognizes the frequency. The ARS is provided by sending the frequency offered from the terminal through the communication path.
However, in a mobile station transmission is performed in the form of not frequency but message passing through a base station and mobile exchange from the terminal so that corresponding frequencies to numbers pushed by the subscriber must be transmitted from the mobile exchange. For this reason, in the mobile exchange, the device for DTMF transmission must be connected, which may affect the communication path when DTMF or new service is provided to the mobile subscriber. In other words, in the CDMA mobile communication system, coding is differentiated with the bit rates of 9.6 kbps, 4.8 kbps and 1.2 kbps, and these sampling rates prevent the DTMF tone from being transmitted directly. This requires DTMF switch connection and release from the subscriber control block.